Peanut Butter and Banana Frosting Be The First To Review By Anonymous recipe Better than a peanut butter and banana sandwich! Use with a yellow cake. Peanut Butter and Banana Frosting Ingredients 1/2 cup margarine1/2 cup shortening1 cup peanut butter3 tablespoons evaporated milk1 teaspoon vanilla extract1/2 teaspoon butter flavored extract1 pound confectioners’ sugar2 bananas Instructions 1 Combine margarine, shortening, peanut butter, milk, vanilla, and butter flavoring. Add confectioners’ sugar and beat until creamy. Add more milk, if needed, 1 teaspoon at a time. 2 Spread icing over one layer of a yellow cake. Slice bananas on top. Place second layer on top and frost top and sides.